Yeah, it's Black Butler, and yeah, Corsets are typically only for women. In this particular arc though, they're trying to track down a Jack The Ripper-esque serial killer who goes exclusively after women, and in order to do so, they dress him up as a woman and go undercover.

The reason why thousands of fangirls started pairing a grown up man with a 12/13 year old boy.
If you start watching that anime/maga, keep away from every site that feaatures fan art of those two, you will get on the goverment watch list.